The present invention relates to the pretreatment and cleaning of surfaces such as the surfaces of cooking equipment, for example, ovens or broilers (preferably ovens or broilers used commercially, as, for example, in a fast food restaurant), that are subject to heat and are liable to soiling by organic food deposits, especially baked-on organic food deposits. The soil deposited on these surfaces typically consists of a complex mixture of natural fats and other organic deposits from the cooking of food. When heated at normal oven or broiler operating temperatures, this soiling matter is often converted into a polymeric mass in which part of the organic material is carbonized.
Removal of this soil is a considerable problem, especially in restaurants where ovens and broilers are used to cook large amounts of food and soil levels are high. Removal of badly burned soils requires the use of highly alkaline, unsafe oven cleaners (typically based on sodium or potassium hydroxide) and/or laborious scrubbing and scraping. The time, effort, and safety risk involved are such significant deterrents to regular cleaning that restaurant ovens, broilers, and other surfaces liable to soiling by organic food deposits are often chronically soiled.
Oven cleaners containing alkali materials less alkaline than caustic soda are known. For example, U.S. Pat. No. 3,658,711 issued Apr. 25, 1972 to Mukai et al., and British Patent No. 1,275,740 published May 24, 1972 disclose the use of alkali metal phosphates combined with an amine component or "enhancing agent" and other optional ingredients such as, for example, surfactants, abrasives, thickening agents or suspending agents. However, such oven cleaners are not very effective in saponifying baked-on fat and consequently are not efficient oven cleaners. Further, such products, when applied to soiled oven surfaces, must attack the soiling matter from the Outer surface, while the most severe polymerization and carbonization are generally present at the interior of the soil layer, adjacent to the oven wall.
Oven pretreatment compositions, which are applied to oven surfaces prior to soiling and then removed after soiling, are also known. For instance, U.S. Pat. No. 4,877,691 to Cockrell discloses a composition comprising an inorganic thickening agent and an alkaline, water-soluble inorganic salt. The composition forms a food-safe coating that adheres to all portions of an oven surface and, in a clean oven, remains continuous as the coating dries. The resulting dried film is resistant to scuffing and chipping at typical oven temperatures and prevents fats and other food soils from burning onto exposed oven surfaces. After soiling, the film and the accompanying spattered food soils are easily removable with water or an aqueous solution.
However, the composition of U.S. Pat. No. 4,877,691 typically dries to form a film which may be hazy or opaque in appearance. This hazy or opaque appearance tends to obscure, at least to some extent, the original surface of the oven and may be considered aesthetically undesirable by some users. Thus, there is a need in the art for a composition that dries to form a more transparent film.
U.S. Pat. No. 5,137,793 to Cockrell discloses another oven pretreatment composition comprising an inorganic thickening agent, an alkaline, water-soluble inorganic salt, and a high-boiling organic component. This composition forms a food-safe coating that adheres continuously to all portions of an oven surface, including areas which are already soiled by food deposits, as the coating dries. The resulting dried film is resistant to scuffing and chipping at typical oven temperatures, is substantially transparent after drying, and prevents fats and other food soils from burning onto exposed oven surfaces. After accumulating additional food soils, the soiled film is readily removed by contact with water or an aqueous solution.
At oven temperatures above 475.degree. F., however, the carbon-carbon backbone of the high-boiling organic component of the composition of U.S. Pat. No. 5,137,793 is subject to breakdown. The resulting smoking and browning usually causes the film to become opaque, depending on the length Of time after application, the temperature, and the degree of soiling. This hazy or opaque appearance, as explained above, is considered aesthetically undesirable by some users.
Thus, there is a need in the oven cleaning art for a pretreatment composition which can be applied to a desired clean or soiled surface to form a continuous coating, which dries to form a substantially transparent and continuous film, which remains substantially transparent at elevated oven temperatures such that the original oven surface remains visible, and which is quickly and easily removed by contact with water or an aqueous solution after accumulating additional food soils during oven use.